This invention relates to a self-sealing door assembly for a coke oven, comprising a door frame affixed around the oven opening, the surfaces of the frame facing the oven defining a gap which is filled with heat insulating material, and the outer front surface of the frame cooperating with sealing strips on the body of the door.
In such types of door assembly for coke ovens, the body of the door usually has on the oven side iron sealing strips which are mostly adjustable and are supported on the outer front surface of the door frame, so as to effect sealing. The sealing is necessary so as to prevent any emissions from within the chamber of the coke oven or to limit such emissions to a small amount, and to protect the door components from the thermal stresses associated with these emissions. The door frame is also included in the parts which undergo thermal stress, because it has surfaces on the side facing the oven which lie behind the sealing strips and which are therefore subject to the effects of heat. To take account of these conditions, a gap is provided between the surfaces of the door frame facing the oven and the brick oven opening, this gap being filled with heat insulating material.
It is known that the door frames can be produced with various profiles, so as to compensate for thermal stresses. So-called block frame profiles work better than ribbed profiles. It is also known that the effect of high temperatures on cast iron of a certain composition leads to a conversion of the carbide carbon in ferrite and graphite. This conversion is associated with a reduction in the strength factors and therefore leads to damage to the door frame, which can be prematurely destroyed. In order to meet this problem, the door frame is made in such a way that it can be replaced.
This invention proceeds from the appreciation that the measures taken hitherto do not take sufficient account of the thermal stresses of the door frame. Between the periods in which the oven chamber is loaded, an approximately constant temperature gradient is formed in the door frame profile. This means that the temperature difference between the heat radiated from the hot part of the oven chamber and the heat of the door frame radiated into the atmosphere is approximately constant. The oven locks and therefore also the seals can be successfully adjusted to this temperature gradient, so that during coking time the emissions are greatly reduced. However, if the charging process is included then there occurs a drastic change in the temperature gradient. This is above all to be attributed to the high thermal stress of the surfaces of the door frame on the oven side during compression of the coke. It leads to one-sided heating of the door frame. This results in lengthwise distortion which has become known by the phrase "waisting".
Attempts have been made by structural means to secure the door frame to such an extent that waisting is at least limited. Shims and clamps, which are used in practice, serve this purpose. However, results by this means are comparatively ineffective with regard to distortions caused by temporary spontaneous heating of the parts facing the oven. These distortions cause the above-mentioned joint of the frame to become unsealed, and moreover distort the door frame to such an extent that the oven locks no longer seal. Particularly during the period of the first coking phase, increased emissions occur.
The object of this invention is to stabilise the temperature gradient in the door frame during the charging process, so as to eliminate the above-mentioned disadvantages.